Porous inorganic materials having a framework of —Si—OH—Al— groups have been widely used in the field of porous molecular sieve catalysts because they have abundant pores, large specific surface area, and many active sites and acid sites.
This porous molecular sieve catalyst is used in, for example, heterogeneous catalytic reactions, such as various oxidation/reduction reactions, including catalytic cracking reactions, isomerization reactions and esterification reactions, particularly heterogeneous catalytic reactions requiring thermal stability under a severe atmosphere of high temperature and humidity. In this case, however, the catalyst has problems in that, when it is placed in a steam atmosphere of more than 500° C., dealumination of its tetrahedral framework will occur, leading to its structural breakdown, and at the same time, the acid sites of the catalyst will be reduced, resulting in a rapid reduction in catalytic activity. Additionally, since high mechanical strength is required for these microporous molecular sieve catalysts in order to be used in massive fluidized catalytic petrochemical processes for naphtha catalytic cracking, inorganic complex and matrix(clay) are used for producing spherical catalysts in these area.
Therefore, since microporous molecular sieve catalyst comprising many components such as bonding agent, matrix, and porous molecules, maintaining thermal-stability for the respective component is one of the most important factors to produce proper microporous molecular sieve catalyst. For example, the collapse of matrix structure, which is used for microporous molecular sieve catalyst, decreases drastically the reaction rate of naphtha catalytic cracking.
In other hand, in order to achieve high yield of ethylene and propylene in naphtha catalytic cracking process, it is required to control the characteristic of acid site in microporous molecular zeolite. If the amount of acid site is large or strength of acidity is strong relatively, dehydrogenation reaction is faster, and so the yield of saturated hydrocarbons such as methane and aromatics such as benzene, toluene and xylene, increases.
On the other hand, if the amount of acid site is small or strength of acidity is weak relative, conversion of hydrocarbon decreases and so light olefins decrease.
As mentioned above, in order to produce light olefins effectively from hydrocarbons such as naphtha by catalytic cracking using catalyst, many characteristics of catalyst are required. Specially, the thermal-stability is considered to be the most important factor because the catalytic cracking catalyst is operated in conditions of high temperature and high humidity. Many researches have been proposed to increase thermal-stability.
Regarding these methods, U.S. Pat. No. 5,039,644 discloses a method using phosphate in preparing a catalyst which is stable in high temperature, which comprises 0.5˜15 wt % of P2O5 imbedded in porous metal oxides such as TiO2, ZrO2, TiO2—ZrO2 mixture, TiO2—Al2O3 mixture, or ZrO2—Al2O3 mixture. However, this patents does not explain how to achieve high yield of light olefins from catalytically cracking hydrocarbons using zeolite.
U.S. Pat. No. 4,977,122 discloses a hydrothermally stable catalyst, which comprises: (a) a crystalline zeolite; (b) an inorganic oxide matrix (e.g., silica, alumina, silica-alumina, magnesia, zirconia, titania, boria, chromia, clay, etc.); and (c) discrete particles of phosphorus-containing alumina also dispersed in said matrix, said discrete particles having been prepared by contacting alumina with a phosphorus compound selected from the group consisting of an alkaline earth metal salt (Be, Mg, Ca, Sr, Ba) of phosphoric acid or phosphorous acid and mixtures thereof.
U.S. Pat. No. 6,835,863 discloses a process for producing light olefins by catalytically cracking naphtha (boiling point: 27-221° C.) using a pelletized catalyst containing 5-75% by weight of ZSM-5 and/or ZSM-11, 25-95% by weight of silica or kaolin and 0.5-10% by weight of phosphorus. However, there is no mention of the specific phosphorus starting material or of the hydrothermal stability of the molded catalyst.
Meanwhile, U.S. Pat. No. 6,211,104 discloses a catalyst for catalytic cracking, which comprises 10-70 wt % of clay, 5-85 wt % of inorganic oxides and 1-50 wt % of zeolite. The zeolite used in the catalyst consists of 0-25 wt % of Y-zeolite or REY-zeolite and 75-100 wt % of pentasil zeolite (SiO2/Al2O3=15-60; selected from ZSM-5, ZSM-8 and ZSM-11 zeolites containing 2-8 wt % of P2O5 and 0.3-3 wt % of Al2O3 or MgO or CaO), in which the starting materials of said aluminum or magnesium or calcium compounds are selected from aqueous solutions of their nitrates, hydrochloride, or sulfates. Particularly, the catalyst is described as showing excellent olefin production even when pretreated in an atmosphere of 100% steam at 800° C. for 4-27 hours. However, in said patent, technology for adjusting/selecting and loading the specific chemical species of P is not disclosed, the added metals are limited to Al, Mg and Ca, and a conventional water-soluble metal salt is used so that the Al, Mg or Ca cations, which are generated during the preparation of the catalyst, can be easily ion-exchanged with the protons of zeolite, resulting in the loss of acidic sites. For this reason, it is believed that it is not easy to prepare the catalyst proposed in said patent under the specified synthesis conditions.
In US publication No. 2005/0020867 A1, the catalyst for light olefin production is disclosed, said catalyst is prepared by the steps comprising that ZSM-5 treated with P2O5 1˜10 wt.% RE2O3 0˜10 wt. %, transition metal (Fe, Co, Ni, Cu, Zn, Mo, Mn) oxides 0.7˜15 wt. % is completed by drying and calcination, and then mixed with clay and inorganic bonding agents (silica, alumina, silica-alumina), followed by spray drying. The present ZSM-5 is silica-rich (higher Si/Al ratio) that may reduce aromatization and hydrogen transfer reaction. However, the silica-rich ZSM-5 is not economic for its complicated synthetic method, weak for matrix performance and structural stability by severe thermal treating with inorganic bonding agents and clay which are not stable at high temperature steaming. It may cause reducing catalytic cracking activity of zeolite.
In the U.S. Pat. No. 6,613,710, P-modified clay 40˜80 wt. %, semi-basic alumina 1˜20 wt. %, and ZSM-5 0.5˜15 wt. % are used for the catalyst of catalytic cracking reaction. P-modified clay are formed from treating clay and phosphoric acid at 15˜40° C. for 1˜16 hours, semi-basic alumina from slurry of sodium aluminate and aluminum sulfate at pH 7.5˜9. The present catalyst yields more LPG in residual oil cracking within b.p. 315˜528° C. This patent is not for host catalyst but for additive catalyst technology of LPG booster, and there is no disclosure of hydrothermal stabilization improvement and production of light olefins.
In U.S. Pat. No. 5,670,037, ZSM-5 modified with rare earth metal, calcined by aluminum phosphate sol is proposed for hydrocarbon catalytic cracking to increase light olefin yield. It is prepared by mixing of P2O5 and zeolite (wt. ratio of P2O5 to zeolite is 1:5˜99) in aluminum phosphate solution, drying, calcining, and steaming. The completed catalyst is made of zeolite 10˜35 wt. %, inorganic oxides (Al2O3, SiO2, Al2O3—SiO2) 5˜90 wt. %, and clay 0˜70 wt. %. Aluminum phosphate solution is used for treating zeolite, and there is no explanation of the yield increment of light olefins without the usage of rare earth metal.
In the U.S. Pat. No. 6,080,698, the pentasil-type zeolite catalyst for production of light olefin by hydrocarbon catalytic cracking is prepared by ZSM-5 (SiO2/Al2O3=15˜60) treated P2O5 1˜10 wt. %, alkaline earth metal oxides 0.3˜5 wt. %, and transition metal oxides 0.3˜5 wt. %. The results with Mg, Ni, Zn, Cu, and Ca for treatment of zeolite are reported, while the result with manganese oxide is not explained. The phosphorus is limitedly used to only modify zeolite with transition metal.
In the U.S. Pat. No. 6,080,303, the zeolite catalyst for production of light olefin by hydrocarbon catalytic cracking is prepared by treating with aluminum phosphate (AlPO4). The catalyst is prepared by 1) making and calcining ZSM-5 with modified with phosphorus, 2) forming AlPO4 by mixing Al(NO3)3 and NH4(H2PO4) at pH 7˜9, 3) treating phosphorus based ZSM-5 with AlPO4 and calcining. For treatment using AlPO4, both of dried state and wet gel state for AlPO4 may be possible. The completed catalyst has a composition comprising of P 0.5˜10 wt. %, AlPO4 1˜50 wt. %, zeolite 5˜60 wt. %, and balanced binder or clay. In the present patent, P and AlPO4 are used to improve hydrothermal stabilization of zeolite, and the advantage of the result of hydrothermal treatment of n-hexane is explained. However, there is no result before hydrothermal treatment, and no explanation of the stabilization technology of binder and clay as P and AlPO4 are only used for treating zeolite.
In US Patent 2006/0011513 A1, the catalyst made of ZSM-5, Beta, Mordenite, Ferrierite, and zeolite (silica/alumina>12), which is treated with the mixed binder of aluminum phosphate salts and metal phosphate salts, is proposed as an additive in FCC process. The metal phosphate salts as binder are selected from IIA group, lanthanoids group, Sc, Y, La, Fe, La, and Ca, and the content of phosphate is more than 5 wt. %, and 4˜50 wt. % is included in typical cases. In this patent, there is not shown chemical structures of phosphate salts, which is not for active sites but for binders. Furthermore, there is also not disclosed of improvement of olefin yield by using zeolite formed with manganese.
In the U.S. Pat. No. 5,380,690, catalyst which comprises clay 0˜70%, inorganic oxides such as Al2O3, SiO2, Al2O3—SiO2 5˜99%, and zeolite 1˜50% is disclosed, said catalyst is pentasil zeolite catalyst with Y zeolite 0˜25%, P2O5 75˜100%. ZSM-5. Said catalyst is prepared by uniformly mixing ZSM-5 modified from Re2O3 1˜30% with aluminum phosphate solution (Al2O3:P2O5=1:1˜3, wt. ratio, P2O5: zeolite=1:5˜99), calcining, and steaming.
In the US patent 2006/0116544, it reports that by treating pentasil type zeolite within rare earth metal and manganese or zirconium with phosphorus, hydrothermal stability and yield of light olefin are improved. It is required that manganese or zirconium is included together with rare earth metal and phosphorus in zeolite in order to improve the yield of light olefin. Furthermore, direct injection of rare earth metal and manganese or zirconium and phosphorus in zeolite is used as treating method. The purpose of this technology is structural improvement like the previous ones, and there are no comments about stabilization of inorganic binders or matrix contents.
In the U.S. Pat. No. 4,956,075, the Y zeolite catalyst treated with manganese and rare earth metal is proposed for hydrocarbon catalytic cracking for gasoline with higher octane number. However, the catalyst has less yield of light olefins and hydrothermal stability than pentasil type catalysts.
Addition of manganese to ZSM-5 may improve hydrothermal stability, reporting in “Studies in Surface Science and Catalysis”, V105, 1549(1996). However, there is only explanation of hydrothermal stability, no explanation for production of light olefins by hydrocarbon catalytic cracking.
In the U.S. Pat. No. 6,447,741, aluminophosphate treated by manganese is used for catalyst of catalytic cracking, while there are no results of synthesis of catalyst and application for hydrocarbon cracking. In addition, in this patent, it is not considered for hydrothermal stability and catalytic characteristics of zeolite, clay and binder.
As explained above, transition metals such as manganese, phosphate and rare earth metals have been proposed to increase thermal-stability of catalysts and high yield of light olefins from hydrocarbon catalytic-cracking. However, there is no previous report which explains systematically how to prepare the catalysts for high thermal-stability and high yield of light olefins. That is, there is no previous report as proposed by the present invention, which describes imbedding acid site of zeolite by manganese, stabilizing inorganic complex and matrix by phosphate and manganese in order to maintain the catalyst activity for long period and increase yield of light olefins. Also, this present invention shows cost-effective procedure for manufacturing catalyst by eliminating complex imbedding step and complex processing spherical catalyst.
As described in above comparative patents, phosphate show high ability to increase thermal-stability of zeolite catalyst. Phosphate increases thermal-stability by stabilizing Al through acting as phosphate ion ([PO4]3−) in —Si—OH—Al— frame which is Bronsted acid site and dealuminated by steam.
However, thermal-stability is affected strongly by how to introduce phosphate into zeolite. In order to introduce phosphate into zeolite to increase thermal-stability, previous methods tried to inject phosphoric acid directly into zeolite. However, large amount of acid sites are lost according to these methods. Another method is to use phosphoric acid and rare-earth metals, such as La, together. In this method, large size of La3+ or phosphoric acid decreases the reaction activity by positioning at entrance of zeolite pore. Additionally since the previous methods tries to make only zeolite itself thermally stable, the problem is that the microporous molecular sieve catalyst made by the zeolite does not have sufficient thermal-stability.
Therefore, the present intention discloses {circle around (1)} a method to stabilize the catalyst for long period in circumstances of high temperature and high humidity, {circle around (2)} a method to maximize yield of light olefins by maintaining acid sites of catalyst after imbedding.